1. Field of the Invention
The present invention relates to a fluorescent endoscope system for simultaneously producing a reflected-light image depicted by reflected light with wavelengths in the visible spectrum and a fluorescence image depicted by infrared radiation.
2. Description of the Related Art
In recent years, an endoscope of which insertional part is inserted into a body cavity for the purpose of observing the alimentary canal extending from the esophagus through the stomach to the small and large intestines or the trachea extending to the lung, or if necessary, of conducting various kinds of treatments using therapeutic instruments inserted into a therapeutic instrument channel has been put to use. In particular, an electronic endoscope having an electronic imaging device such as a charge coupled device (CCD) has been widely adopted because an image can be displayed on a monitor and an operator of the endoscope is little fatigued with manipulation.
Recently, a modality in which a fluorescent substance having an affinity for a lesion such as a carcinoma is administered to a subject to be examined in advance, excitation light for exciting the fluorescent substance is irradiated, and fluorescence emanating from the fluorescent substance is detected.
According to the modality, since intense fluorescence is radiated from a lesion, the presence of the lesion can be judged from the brightness of a fluorescence image. A system adopting the modality is, for example, a system as disclosed in Japanese Unexamined Patent Publication No. 59-40830, for detecting fluorescence emanating from hematoporphyrin that is a fluorescent substance.
In the system disclosed in Japanese Unexamined Patent Publication No. 59-40830, control is provided so that pulsed laser light for excitation and white light for normal observation can be irradiated selectively. Japanese Unexamined Patent Publication No. 7-59783 has disclosed a system enabling observation of fluorescent substances such as chlorin and pheophorbide. In the system disclosed in Japanese Unexamined Patent Publication No. 7-59783, light suitable for exciting a fluorescent substance and light suitable for normal light observation (white light) are irradiated while being switched by a rotary filter.
Prior methods for exciting fluorescent substances include irradiating light with relatively short wavelengths of about 405 nm. When light with the wavelengths is irradiated to a living tissue, the living tissue itself fluoresces. Unless an apparatus exhibiting high spectroscopic precision such as a spectrometer is employed, it is hard to distinguish self-fluorescence from fluorescence emanating from a fluorescent substance.
The, transmittance of light with short wavelengths relative to a living tissue is so poor that a system using hematoporphyrin to be excited by light with short wavelengths may miss the presence of a substance fluorescing in a deep subcutaneous region.
In the prior art, excitation light and white light are irradiated while being switched temporally. Consequently, during irradiation of excitation light, a fluorescence image alone can be produced. During irradiation of white light, a normal light image alone can be produced. There is a large difference in time between the fluorescence image and normal image.